P!nk is no stranger to the top of the charts. She first hit No. 1 in 2001 with her collaboration “Lady Marmalade” which featured Christina Aguilera, Lil’ Kim and Mya, according to Billboard. Ruess, on the other hand, reached No. 1 for the second time with “Just Give Me a Reason.” Last year, fun. hit No. 1 with their breakthrough single “We Are Young” featuring Janelle Monae.

P!nk and Ruess’ collaboration was a surprising match-up when it first premiered in February, which got us thinking: what’s the deal with male/female pop duet hits?

Of course you have your classic partners like Marvin Gaye and Tammi Terrell, but what about those unexpected pairings? The ones that cross genres or even generations, combining their star power to create one great song. In hindsight, some have fared better than others; sometimes, two hot stars pair up but only one of them has the longevity, leaving listeners scratching their heads decades later.

Here’s a look at five unexpected duets that soared to the top of the charts.

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“One” – Mary J. Blige & U2

U2 originally recorded the song in 1991 for their album Achtung Baby, but have gone on to record it many times, including as a benefit single to raise money for AIDS research as part of Bono’s ONE campaign. One of its most interesting inclinations though has to be Mary J. Blige’s cover, which is featured on her 2005 album, The Breakthrough. Instead of doing it alone, she invited the band to help her, combining her soulful voice with Bono’s rock star swagger. Blige may take the lead, but she doesn’t stray too much from the original. Instead she immerses herself into the rock and roll world, even donning a studded vest and showing off her best Pete Townshend windmill for the black and white clip of the song. Even though the duet seemed weird at the time, Mary J has gone on to become a true rocker chick, even covering Led Zeppelin’s “Stairway To Heaven” and performing alongside the Rolling Stones and a Verizon fios promo code charity concert at their 2012 shows.

“I Knew You Were Waiting (For Me)” – Aretha Franklin & George Michael

Why would the Queen of Soul team up with the former Wham! frontman? Well, it was the ‘80s and with one listen of the heavily produced single, you realize the duet is certainly a product of the time. It was 1987 and Michael had just recently topped the charts with “Careless Whisper.” Aretha, on the other hand, hadn’t had a real chart-topper in two decades; in fact, her 1967 classic “Respect” was the first and only time she reached the top of the Billboard Hot 100. Michael, being a fan of Aretha, asked her to appear on the song. He even got her to wear a very Eighties-looking getup, while he shook his denim-clad hips for the video. It ended up being Aretha’s second No. 1 hit on the Hot 100 chart and her first song to hit No. 1 in the U.K. – and she hasn’t had a No. 1 single since. It’s almost as if she really was waiting for him.

“Picture” – Sheryl Crow & Kid Rock

An unlikely collaboration, Kid Rock and Sheryl Crow co-wrote “Picture” together for Kid Rock’s 2001 album Cocky. This marked Kid Rock’s transition from rap to Southern rock, and “Picture” became his first crossover hit, charting No. 4 on the Hot 100 as well as the top 5 on Top 40, AC and the Country singles charts. While Crow was featured on the original version, Kid Rock released the song’s single version with another artist, Allison Moorer, in November 2002. Seeing the success of the song, in January of 2003 Crow’s label permitted that her version with Rock be released; it became one of her biggest singles to date. Crow and Moorer aren’t the only ladies who have sang the track with Rock; country singers Kellie Pickler, Martina McBride, Miranda Lambert, Gretchen Wilson and LeAnn Rimes have also guested on vocals during live performances of “Picture.”

“Don’t Go Breaking My Heart” – Elton John & Kiki Dee

Kiki Dee started as a session singer for Dusty Springfield, but came out of obscurity in 1976 to record one of the most beloved duets of all time. Teaming-up with Elton John not only earned her a No. 1 hit in the U..K (a first for both artists), but a No. 1 single in the United States that spent four weeks at the top of the Billboard Hot 100. Dee, whose real name is Pauline Matthews, went on to record 12 albums and release 39 singles. She would even team up with Elton for another song, this time it was Cole Porter’s “True Love” for his 1993 album, Duets. And sure, John would go on to do a few notable things here and there, but it’s his duet with Kiki Dee that gets everyone up and singing at karaoke.

“I’m Real” – J.Lo and Ja Rule

J.Lo’s girlish vocals coupled with Ja Rule’s smooth raps made this the song of the summer in 2001. Although it had a slow start, “I’m Real” climbed all the way to No. 1 on the Billboard Hot 100 by the time September came around. The song was featured on Lopez’s second album, J.Lo, and saw the pop star embrace her hip-hop roots (remember her fly girl days?). While J.Lo has gone on to act in Hollywood blockbusters, judge American Idol and release many more singles, it’s this one that convinced us all of her staying power. Her second No. 1 after 1999’s “If You Had My Love,” it remains one of her most recognized songs.